Gas turbine engine efficiency is a function of various parameters, among them the temperatures achievable within combustion chambes as well as the amount of air which must be diverted to cool various elements of the engine. Additionally, the structural integrity of an engine is improved if structural loads are carried by elements of the engine which elements are not also subjected to high temperatures and attendant thermal stresses.
In an attempt to raise achievable temperatures within combustion chambers, various metals and alloys have been used in the construction of the chambers. Two such materials which exhibit particularly beneficial heat resistance are oxide dispersion strengthened metals such as thoria dispersed nickel and thoria dispersed nickel chromium alloy, which have melting temperatures of approximately 2500.degree. to 2600.degree. F., and which exhibit high strength characteristics up to temperatures of 2200.degree. F. Thus, these materials would prove useful in the construction of combustion chambers. A major drawback of these and certain other high temperature metallic materials, however, is that they are difficult or impractical to weld. In the case of the thoria dispersed materials, the weld area loses thoria, consequently reducing substantially the strength of the material. The present invention provides a construction arrangement for use in gas turbine engines whereby such materials (and other appropriate materials, e.g. FeCrAl, columbium, etc.) can be effectively applied as liners for combustion chambers without the necessity of welding.
The effective application of such higher temperature operating materials as thoria dispersed nickel or thoria dispersed nickel chromium alloy as a liner within combustion chambers, in addition to enabling higher temperatures to be reached, also allows a reduction in the amount of cooling air required to be directed to the liner during operation. This reduction enables the engine to operate with increased efficiency. The present invention further provides means for effectively utilizing the reduced quantity of cooling air to cool both the inner and outer sides of the combustion chamber liner.
Structural failures in gas turbine engines in the past have often resulted from the subjection of structural load bearing portions of the engine to thermal stresses associated with the high temperatures of combustion. The formation of a combustion chamber in a way that requires the chamber liner (which is directly exposed to the heat of combustion) to carry structural loads associated with the combustion chamber has resulted in such failures. The present invention overcomes these problems by isolating the liner of the combustion chamber from the structural loads associated with the frame encircling the chamber.